FLU 
FLU 
FLU 
750 
sum. There will remain rather more than 
1000°, which is the quantity of caloric which 
existed in the steam without increasing its 
temperature. This experiment cannot be 
made directly; but it maybe made by pass- 
ing a given weight of steam through a me- 
tallic worm, surrounded by a given weight of 
water. The heat acquired by the water in- 
dicates the caloric which the steam gives out 
during its condensation. From the experi- 
ments of Mr. Watt made in this manner, it 
appears that the latent heat of steam amounts 
to 940°. The experiments of M. Lavoisier 
make it rather more than 1000°. 
Bv the experiments of Dr. Black and his 
friends, it was ascertained, that not only wa- 
ter, but all other liquids during their conver- 
sion into vapour, combine with a dose of 
caloric, without any change of temperature; 
and that every kind of elastic fluid, during 
its conversion into a liquid, gives out a por- 
tion of caloric without any change of tempe- 
rature. Dr. Black’s law then is very general, 
and comprehends every change in the state 
of a body. The cause of the conversion of 
a solid into a liquid is the combination of the 
solid with caloric; that of the conversion of 
a liquid into an elastic fluid is the combina- 
tion of the liquid with caloric. Liquids are 
solids combined with caloric; elastic fluids 
are liquids combined with caloric. 'This law, 
in its most general form, may be stated as fol- 
lows: whenever a body changes its state, it 
either combines with caloric, or separates 
from caloric. 
No person will dispute that this is one of 
the most important discoveries hitherto made 
in philosophy. Science is indebted for it en- 
tirely to the sagacity of Dr. Black. Other 
philosophers indeed have laid claim to it; 
but these claims are either without any foun- 
dation, or their notions may be traced to Dr. 
Black’s lectures, as their opinions originated 
many years posterior to the public explana- 
tion of Dr. Black’s theory in the chemical 
chairs of Glasgow and Edinburgh. 
111. A very considerable number of bodies, 
both solids and liquids, may be converted into 
elastic lluids-by heat ; and as long as the tem- 
perature continues sufficiently high, they re- 
tain all the mechanical properties of gaseous 
bodies. Ft is exceedingly probable, that if 
we could command a heat sufficientlv in- j 
tense, the same change might be produced j 
on all bodies in nature. This accordingly is 
the opinion at present admitted bv philoso- 
phers. But if all bodies are convertible into 
elastic fluids by heat, it is exceedingly pro- 
bable that all elastic fluids in their turn might 
be converted into solids or liquids, if we could 
(expose them to a sufficiently low tempera- 
ture. In that case, all the gases must be 
supposed to owe their elasticity to a certain 
dose of caloric : they must be considered as 
compounds of caloric with a solid or liquid 
body. This opinion was lirst stated by 
Amontons, and it was supported with much 
ingenuity both by Dr. Black and Lavoisier, 
and his associates. It is at present the pre- 
vailing opinion; and it is certainly supported 
not omy by analogy, but by several very 
striking facts. 
If its truth is admitted, we must consider 
all the gases as capable of losing their elasti- 
city by depriving them of their heat: they 
differ merely from the vapours in the great 
eoki vvhic.i is necessary to produce this 
change. Now the fact is, that several of the 
gases may be condensed into liquids by low- 
ering their temperatures. Oxynmriatic acid 
gas becomes liquid at a temperature not 
much under 40°; and at 32° it even forms 
solid crystals. Ammoniacal gas condenses 
into a liquid at — 45°. None" of the other 
gases have been hitherto condensed. 
It is well known, that the condensation of 
vapours is greatly assisted by pressure ; but 
the effect of pressure diminishes as the tem- 
perature of vapours increases. It is very 
likely that pressure would also contribute 
to assist the condensation of gases. If has 
been tried without effect indeed in several of 
them. Thus air has been condensed till it 
was heavier than water; yet it showed no 
disposition to lose its elasticity. But this may 
be ascribed to the high temperature at which 
the experiment was made relative to the 
point at which air would lose its elasticity. 
At the same time it cannot be denied, that 
there are several phenomena scarcely recon- 
cilable to this constitution of the gases, in- 
genious and plausible as it is. One of the 
most striking is the sudden solidification 
which ensues w hen certain gases are mixed 
together. Thus when ammoniacal gas and 
muriatic acid gas are mixed, the product is a 
solid salt; yet the heat evolved is very incon- 
siderable, if we compare it with the difficulty 
of condensing these gases separately, and the 
great cold which they endure before losing 
their elasticity. In other cases too, gaseous 
bodies unite, and form a new gas, which re- 
tains its elasticity as powerfully as ever. 
Thus oxygen gas and nitrous gas combined 
form a new gas, namely, nitric acid, which is 
permanent till it comes into contact with 
some. body on which it can act. 
FLUOR- ALBUS. See Medicine. 
Fluor-spar. See Fluat of Lime. 
The principal use of fluats is for smelting 
ores, where they act as very powerful fluxes, 
and on this account are much valued. They 
are found in various countries, particularly 
Sweden, and some other northern countries 
of Europe. From this quality of melting 
easily in combination with other earthy mat- 
ters, they have got the name of floors. 
“ The resemblance between the coloured 
floors and the compositions made of coloured 
glass (says Cronstedt), has perhaps contri- 
buted not only to the floors being reckoned 
of the same value with the coloured quartz 
crystals, by such collectors as only mind 
colour and figure, but to their also obtaining 
a rank among the precious stones in the apo- 
thecaries’ and druggists’ shops.” Mr. Fa- 
broni observes, that the combination of cal- 
careous earth with the sparry acid is almost 
always transparent: it often crystallizes in 
regular cubes, sometimes single from one line 
j to two inches in diameter, and sometimes of 
j an indeterminate figure. They are some- 
! times of a blue colour; others are purple like 
j amethysts; some are of a brown colour, 
i others opaque. M. Magellan says, that 
j fiuors in general have this singular property, 
that on being melted by the flame ofthe blow- 
pipe, together with gypsum, the product re- 
sulting from both is all formed with facets on 
the outside; but if melted with terra ponde- 
rosa, its surface is quite round or spherical. 
FLUORIC ACID. The mineral called 
fluor, or fusible spar, and in this country 
Derbyshire spar, was not properly dislin-- 
guished from other spars till Margraff pub- 
lished a dissertation on it in the Berlin Trans- 
actions for 1768. He first proved, that it 
contained no sulphuric acid, as had been for- 
merly supposed: he then attempted to de- 
compose it, by mixing together equal quanti- 
ties of this mineral and sulphuric acid, and 
distilling them. By this method he obtained 
a white sublimate, which he supposed to be 
the fluor itself volatilized by the acid. lie 
observed with astonishment, that the glass 
retort was corroded, and even pierced with 
holes. Nothing more was known concerning 
fluor till Scheele published his experiments 
three years after, by which lie proved that it 
is composed chiefly of lime and a particular 
acid, which has been called fluoric acid. 
The composition of fluoric acid is equally 
unknown with that of muriatic acid. Mr. 
Henry tried in vain to decompose it by- 
means of electricity. It is always obtained 
from fluor spar, in winch mineral it is found 
in abundance. For the investigation of the 
properties of this acid, we are indebted 
chiefly to Scheele and Priestley. 
1. It may be obtained by putting a quan- 
tity of the spar in powder into a retort, pour- 
ing over it an equal quantity of sulphuric 
acid, and then applying a very gentle heat. 
A gas issues from the beak of the retort, 
which may be received in the usual manner 
in glass jars standing over mercury. This 
gas is fluoric acid. 
The acid may be obtained dissolved in 
water by luting to the retort a receiver con- 
taining water. The distillation is to be con- 
ducted with a very moderate heat, not only 
to allow the gas to condense, but also to pre- 
vent the fluor itself from subliming. After 
the process, provided a glass retort lias been 
employed, a crust of white earth is found in 
the receiver, which has all the properties of 
silica. 
Scheele supposed that the silica produced 
was formed of fluoric acid and water; and 
Bergman adopted the same opinion. But 
Wiegleb and Buccholz showed that the quan- 
tity of silica was exactly equal to what the 
retort lost in weight ; and Meyer completed 
the proof that it was derived from the glass, 
by the following- experiment. He put into 
each, of three equal cylindrical tin vessels a 
mixture of three ounces of sulphuric acid 
and one ounce of fluor, which had been pul- 
verized in a mortar of metal. Into the first 
he put one ounce of pounded glass; into the 
second the same quantity of quartz in powder; 
and into the third nothing. Above each of 
the vessels he hung a spunge moistened with 
water, and having covered them, lie exposed 
them to a moderate heat. The sponge in 
the first cylinder was covered with the crust 
in half an hour ; the sponge in the second in 
two hours; but no crust was formed in the 
third, though it was exposed several days. 
In consequence of this decisive experiment, 
Bergman gave up his opinion ; and wrote an 
account ot Meyer’s experiment to Morveau, 
who was employed in translating his works, 
to enable him to correct the mistake in his 
notes. 
Soon after the discovery of this acid, diffi- 
culties and doubts concerning its existence 
as a peculiar acid were started by some 
French chemists. To remove these objec- 
